Changes in glutamine synthetase in harvested asparagus spears: an opportunity for genetic modification?

摘要

Glutamine synthetase (GS) [glutamate-ammonia ligase] content in asparagus spear tissues after harvest was investigated as a prelude to the genetic modification of the crop. Two forms of GS were identified in asparagus, associated with either the cytosol or the plastids. The 2 enzymes have distinct kinetic properties and contain polypeptides of different sizes. The abundance of the 2 GS forms changed as spears were held in the dark at 20℃ for 5 d after harvest. The cytosolic enzyme activity declined immediately after harvest before rising rapidly 4-5 d after harvest. Ammonia also increased 4-5 d after harvest. Plastid GS enzyme activity declined and chlorophyll content decreased in the spear tips throughout the 5 d postharvest period. The possibility of overexpressing GS in genetically modified asparagus tissues in order to assimilate the ammonia that is produced after harvest is discussed and rejected.